In the extrusion of metals, particularly aluminum, the process starts with a metallic log. These logs come in various diameters depending on the size of the extrusion press. A log is loaded into an oven and in the aluminum industry, heated to a temperature of between 800 and 900 degrees. The log then goes from the oven into a log shear and is cut to predetermined length depending on the type and length of extrusion to be manufactured.
The sized logs, called billets, are then transferred by a conveyor to a charger for an extrusion press which, in turn, loads the billet onto a billet loader. Next, the billet loader places the heated billet into a cylinder, which is referred to as the container. The container is moved to a position where the container seals against a die ring at the face of the extrusion press. A hydraulic ram pushes the heated billet through the container.
The ram saves the billet through the container into the die ring which holds a die for the specific shape of the extruded product. The process of pushing the aluminum through the container and die is called extruding. Depending on the shape of the die, various items can be extruded from the hot aluminum billet.
The oxides and other impurities in the aluminum are typically on the radial surface of the billet. These impurities and oxides end up in the butt end of the billet. If the butt end of the billet were not removed from the billet prior to loading another billet, the impurities and oxides would find their way into the extrusion. Therefore, it is necessary to remove the butt end before the next billet is loaded into the container and the extrusion press.
The butt shearing step takes place after the ram has pushed the billet substantially through the die. The ram then goes back out of position and the container is withdrawn. The butt shear comes down and shears off the butt end which includes all of the oxides, scales and other impurities. The butt end of the billet is then transferred to a scrap bin. Some butt shears require a separate step to remove the butts which can stick to the blade.
During the extrusion process, a run out table is used to support the hot extruded product. However, some extruding operations use a puller connecting directly to the extruded forms which pull the extrusion out onto a table. One advantage of using a puller is that it groups and keeps the sections from running together. Another advantage is that the extrusion can be run out faster. After the extrusion has been pulled out to its entire length, an extrusion shear or an operator using a torch may cut the extrusion prior to starting a new extrusion.
After the item is out on the extrusion table, it is then cooled to approximately room temperature and then stretched to remove kinks or other deficiencies. This stretching is typically one percent of the length.
In the extrusion process, dies may either be hollow or solid. In order to extrude a hollow webbed member, such as a tube, the die typically has a cap and a mandrel and the heated aluminum will flow around the webs of the mandrel and through the die to create a hollow shape. These dies can also be called feeder dies. The cap holds or supports an inner section to allow hollow shapes to be formed.
Extrusion dies of either the hollow or solid type typically have different size openings and the hot aluminum can go through larger openings faster than smaller openings. In order to compensate for this problem, the dies have varying length bearing surfaces. A bearing surface is a tapered entrance in which the aluminum flows as it moves through the die. The longer the bearing, the slower the feed. Therefore, when simultaneously extruding large and small shapes, the bearing surfaces need to be adjusted so that the extruded items runs out onto the table uniformly.
The pressure of the ram against these dies require the dies to be adequately supported and held together. A backer and bolster are included with the die arrangement to support and add mass to the die. The die ring holds the die, backer and bolster together in the proper relative position.
The numerous problems associated with the use of prior art shear blade designs are described below:
1. The known shear blades have typically had a cutting edge angle of approximately 15 degrees on the bottom side which comes down in contact with the butt. The top of the butt is smashed down as the blade pushes the butt downward across the face of the die in a tearing action. The thickness of the butt has to be sufficient to resist the severe deformation during this cycle. These butts are typically one inch to one and one-half inch depending on the type of die. This smashing of the butt is a larger problem with hollow dies. The hollow shape is deformed onto the die face causing sealing problems when the container is moved forward for the next push. When extruding small solid shapes, the relatively small contact areas between the spent billet and the butt enables the shearing device to shear off the butt directly at the die face, therefore, the typical problems with deformation are not as apparent.
2. As the butt is being sheared at the face of the die, aluminum is pulled from the ports of both hollow and feeder plate dies which leave voids to entrap air when the next billet is pressed against the die. A burp cycle is used to try to displace the air, but air blisters still appear on a large portion of extrusions using the above dies. A burp cycle is performed by backing the container away from the press after initially sealing the container to the press to let air out and then the container reseals against the press.
3. Extensive aluminum build-up on the face of die, die ring, and container face is caused by the tendency of the butt shear blade to be forced away from the die during the shearing operation. Additionally, prior art shear blades tend to tear the butt off rather than clearly shearing the butt off. Thus, the aluminum left on the die face is rough and uneven. When the container, holding another billet comes into contact with the aluminum left on the die face, air voids are created between the billets. These air voids cause blisters in the extruded products.
4. The uneven sealing surface, caused by the partly displaced aluminum, can cause the container to cock in various planes as it attempts to seal against the die face. This creates havoc when using a fixed dummy block fastened to the die end of the ram. Many fixed dummy blocks have been broken or mutilated as it starts to enter the container when the container is not in alignment. The dummy block is the connection between the ram and the billet.
5. In the use of prior art, butt shear blades often causes the butt to remain stuck to the die face or to the shear blade. A visual inspection after the shearing operation is required to make sure the butt is cleared for the container to seal. If not inspected, and the container attempts to seal on a butt, the container cylinder rods may be bent, inflicting great damage to the press and a consequent loss of production time and the incurrence of large expenses for repairs. Auxiliary devices to knock off butts, and where applicable, sensitive pressures switches, have been utilized on some presses to attempt to minimize the damage, but these solutions are expensive and unreliable. The uncertainty over whether the butt has been cleared from the die or butt shear blade has prevented the use of an automatic cycle on extrusion presses thereby increasing the need for labor and the cycle time, with the result of lost profits.
An object of the present invention is therefore to provide a new and improved butt shear blade design, which overcomes these and other problems.
It is a further object of the present invention to provide a virtually "stick-free" blade for peeling or cleanly shearing butts from spent billets.
It is a further object of the present invention to provide die ring alignment prongs attached to a shear blade which position the die ring and the die prior to the butt shearing operation.
It is a further object of the present invention to mount said blade so that 3/32"-1/8" if material is left on the die face thereby allowing the blade to cut through the aluminum present on both sides of the cutting edges, thereby leaving a smooth aluminum face on the die and eliminating air cavities on the face of the die.
It is a further object of the present invention to eliminate the burp cycle in an automated extrusion operation.
It is a further object of the present invention to reduce scrap aluminum by allowing a reduced thickness of butt to be sliced from a billet.
It is a further object of the present invention to provide automatic shearing of the butt without the need of an operator.
It is a further object of the present invention to eliminate costly down time and bending of container cylinder rods.
It is a further object of the present invention to provide a butt shearing device which greatly reduces the need to clean the die and container surface.
These and other objects of the present invention are attained by the provision of an improved shear blade to slice or peel the butt end of the billet from the die face in an extrusion operation. In a preferred embodiment of the present invention the cutting edge of the shear blade is provided with a 35 degree wedge angle between the die side of the blade and the container side of the blade. This angle allows minimum resistance while cutting and causes peeling or clean shearing as the sheared butt peels or curves away from the blade. This angle also tends to keep the butt shear blade from moving away from the die during the shearing operation.
In a preferred embodiment, the blade has a maximum vertical length of 1 inch for the front and rear cutting surfaces. This dimension tends to reduce the area of contact and friction during the cutting.
The improved shear blade of the preferred embodiment includes a supplementary relief angle on the container side of the blade which is less than the cutting edge angle. This arrangement ensures that the sheared portion of the butt is not in contact with the blade.
The shear blade of the preferred embodiment includes alignment prongs to keep the cutting ring and die edge from coming into contact with the die. The projection of the prongs below the cutting edge keeps the blade from hitting the die ring and die as well as allowing for a predetermined thickness of remainder of billet to be left on the die face.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.